IPM event handler to do an uninstall/install

[isc-tleavitt]

Use case: class deleted from IPM package in branch A
Switch to branch B which still has class - gets reloaded
Back to branch A - class is in IRIS and gets reexported on zpm "load"

[isc-tleavitt]

Alternatively, could pick up deletes/renames and handle them appropriately in the IPM event handler as well.